Plasticized polyvinyl acetal resin



atented ept. ll l$45 PLASTICIZED P01. z i

ACETAL nnsm No Drawing. (lriginal application November 2, 1937, Serial No. 172,441. Divided and this application January 8, 1942, Serial No. 426,004

1 Claim.

Our present invention relates to plastic material to be employed as a sandwich material in the manufacture of laminated safety glass and the like. As is well known to those skilled in theart, polyvinyl acetal resin, i. e., a material made by condensing an aldehyde with a partially hydrolized polyvinyl acetate such as the resin described in the patent to Morrison et al., Reissue No. 20,430, dated June 29, 1937, apears to be an excellent, if not the best material, known for the purpose mentioned provided it is mixed with a satisfactory plasticizer, but its utilization has been retarded by the difllculty which has been experienced in discovering a plasticizer which will give to the final product all of the necessary properties.

These acetal resins vary in the proportion of the degree of hydrolysis of the ester and the degree of combination of the aldehyde. For instance, the molecules of a satisfactory resin made with formaldehyde may be considered to be made of 82% acetal, 8% hydroxyl groups, calculated as polyviny alcohol, and 10% acetate by weight as analyzed. Another satisfactory resin contains 2% or less of acetate, 16 to 20% hydroxyl groups figured as alcohol and the balance acetal formed with butyraldehyde. The difierent resins of which the foregoing are only two examples have difierent properties according to the proportion of the three substituents mentioned and the particular aldehyde employed.

As explained in a companion application of.

Elmer R. Derby, Serial No. 172,443, filed November 2, 1937, plasticizers which are as near the point of incompatibility with a particular resin in the quantity employed are more effective to produce a satisfactory plastic. It has been further discovered that, as explained in a companion application of Elmer R. Derby, Serial No. 172,442, filed November 2, 1937, that certain other plasticizers which are by themselves incompatible with a particular resin in effective quantities may be rendered compatible by the presence of small quantities of plasticizers which are miscible both with resin and with the immiscible or incompatible plasticizer; and that they unexpectedly produce excellent safety glass. Apparently the best, results are produced with plasticizers which are normally incompatible provided they can be rendered compatible. Furthermore the different plasticizers have difierent eiIects on the final product, for instance increase in water resistance, solubility in the resin, adhesive strength at high or low temperatures, etc.

We have discovered that certain esters, conveniently called mixed molecule esters, are par ticularly useful for plasticization of these and similar resins, because it is possible to vary the chemical composition of the ester employed, and thereby to control the physical properties of the material produced when the mixed ester is combined with the polyvinyl acetal resin. By a mixed ester we mean a polycarboxylic or a polybasic acid to which have been attached by esterification the radicals of two difierent substances. For instance a polycarboxylic acid may be combined with difierent monohydric alcohols. The above description is used merely as illustration as other combinations will be readily apparent to those skilled in the art. We have discovered that by employing these mixed molecule esters, it is possible to employ a plasticizer which in the proportions used is just below the point of incompatibility with the particular resin employed, and thus obtain desirable physical properties in the safety glass.

In making up a suitable plasticizer the component elements of the mixed molecule ester are chosen with particular regard fortheir effects on the plasticized mixture. For instance, we have dicovered that the presence of a radical of butyric or phthalic acid improves the water resistance.

The following are specific examples of mixtures embodying my invention:

1. Butyraldehyde resin as described above100 pts. N-Butyl-iso-butyl phthalate-90 pts. Di-

N-butyl phthalate when used in these proportions gives a soft plastic which has poor impact strength at 120 F. Di-isobutyl phthalate gives poor cold and hot break in these proportions.

2. The same resin as Example 1-100 pts. Butyl-hexyl phthalatepts. Dihexyl phthalate gives an oily product when used in these proportions.

When used in laminated glass each of the materials produced in accordance with the foregoing examples give substantially equal hot and cold break tests.

Where, in the preparation of the mixed molecule ester, it is desirable to use other than the exact chemical'equivalent of two alcohols or two acids, it is obvious that the resulting reaction product will consist of a mixture of the mixed moleculeester and the unmixed ester of the constituent in excess. In these cases, the resulting plasticizer should be used as a mixture of the mixed molecule ester and the unmixed ester. In cases where the two acids or alcohols are used in equivalence, there will also be present unmixed esters to satisfy equilibrium conditions; these may either be removed by appropriate fractionation, or in some cases may be left in the plasticizer.

The present application is a division of our prior application Serial Number 172,441, filed November 2, 1937, now Patent No. 2,294,353. 

